Oh man, had so many fights about this. Had some slam the door of my car and leave because I tried honestly to understand why TF he couldnt be on time. Its always lies/detracts from the topic masterfully. I would tell them, no problem man, if its 40mins instead of 20min, tell me 40 just dont leave me waiting again (which also leaves one VERY exposed). Approached this problem from many aspects, like call me before you leave or lets meet an hour or so after whatever is keeping you so you can be on time and I dont have to wait etc... etc... It doesnt matter. If youre dealing with a person who doesnt give a sh*t about you/your time(which is the same basically) and is at the same time always in complete denial about his actions, youre not gonna win. And most are also great manipulators, can act so sweet and apologetic but in the end you realize youre back in the same cycle, again waiting on them like a jackas*.
Sure dude, Im also like that. Or at least were. But the problem with your post is that youre coming off an assumption that the dealer is a sane,self-reflecting, rational or any other word that is appropriate, person. And so so many are not. Either deliberately or just plain delusional. I honestly have trouble understanding it, but no amount of reasoning or explaing time and responsiblity to them will change their actions. They block it from their mind, dont want to talk about it, etc..they never think "humm maybe im not being nice to him by always being late". They have their rationalization worked out to a T or get angry, any time constraints/demands regarding their dealings are pushed from their minds and just operate with a absolute dont give a rats a*s. Youll always get a something like "yeah sure man, sorry, will be on time next time".
Then there is also the always present problem of limited number or connects in any certain area. You can play pick and choose for only a limited number of times until youre out. When I had many connects and the one I was meeting was (again) late I would leave lots of times. If its not a big dealer, its one of the best things you can do in a way cause it makes him realize how much he actually needs you. But most dont care really and might drop you as a customer if you keep leaving.
One thing Ive noticed that might help is to make the meeting as close to the current time as possible cause otherwise there are million things that can keep them or just plain forget, often it helps to make the deal at a certain time and not like in 1hour or 40mins or sth. They always act dumb and says sh*t like "its not 40mins? now" when its way past that. "Didnt we talk at x.xx?". And if you show him the phone and time, they just get pissed how they have sh*t to do and cannot always be on time. I guess it also helps that you dont say "im just leaving". always say "im already there" "or on the way, almost now" so they dont think they have time for other stuff. Maybe try to make yourself a bit distinctive from others and be nice,so he might care at least a little bit if hes late with you, can help a lot.